Move Follows Decompression Incident Involving A Southwest B737

As reported by ANN Monday, the FAA has gone forward with an emergency AD for three series of Boeing's workhorse 737 single aisle airliners.

AD 2011-08-51 has been sent to owners and operators of The Boeing Company Model 737-300, -400, and -500 series airplanes. This emergency AD was prompted by a report indicating that a Model 737-300 series airplane experienced a rapid decompression when the lap joint at stringer S-4L between body station (BS) 664 and BS 727 cracked and opened up. Investigation showed that the cracking was located in the lower skin at the lower row of fasteners. The airplane had accumulated 39,781 total flight cycles and 48,740 total flight hours. This condition, if not corrected, could result in an uncontrolled decompression of the airplane. Because the lap joint and tear strap spacing configuration is the same on Model 737-400 and -500 series airplanes, these airplanes may be subject to the identified unsafe condition.

The FAA has reviewed Boeing Alert Service Bulletin 737-53A1319, dated April 4, 2011. The service bulletin describes procedures for external eddy current inspections of the lap joints at stringers S-4R and S-4L, along the entire length from body station (BS) 360 to BS 908. If a crack indication is found, the service bulletin specifies either confirming the crack by doing internal eddy current inspections, or repairing the crack. As an alternative to the external eddy current inspections, the service bulletin provides procedures for internal eddy current and detailed inspections for cracks in the lower skin at the lower row of fasteners at stringers S-4L and S-4R. The service bulletin specifies contacting Boeing for crack repair instructions.

Southwest B737-300

The emergency AD was issued after the FAA evaluated all the relevant information and determined the unsafe condition described previously is likely to exist or develop in other products of these same type designs.

FMI: www.faa.gov